In general, a compressor is for enhancing a pressure of refrigerant vapor in order to easily condense refrigerant vapor evaporated from an evaporator. By operation of the compressor, refrigerant repeats condensation and evaporation processes and circulates in a refrigerating device, thereby transmitting heat from a cold part to a warm part.
Among several types of the compressor which are nowadays used, a reciprocating compressor is the most widely used. The reciprocating compressor compresses vapor by a piston which moves up and down in a cylinder thus to enhance a pressure. Since a compression ratio of the reciprocating compressor can be varied by varying a stroke voltage applied to the reciprocating compressor, the reciprocating compressor can be used in controlling a variable refrigerating capacity.
However, since the reciprocating compressor compresses vapor by converting a rotation movement of a motor into a linear movement, a mechanical converting device such as a screw, a chain, a gear system, a timing belt, and etc. for converting a rotation movement into a linear movement is absolutely necessary. According to this, an energy conversion loss is great and a structure of a device becomes complicated. Therefore, recently, a linear compressor using a linear method that a motor itself has a linear movement is being used.
The linear compressor does not require a mechanical conversion device since a motor itself directly generates a linear driving force. In the linear compressor, a structure is not complicated, an energy conversion loss is reduced, and noise can be greatly reduced since a connection portion where friction and abrasion are generated does not exist. Also, in case of applying the linear compressor to a refrigerator or an air conditioner, a compression ratio of the linear compressor can be varied by varying a stoke voltage applied to the linear compressor, so that the linear compressor can be used in controlling a variable refrigerating capacity.
FIG. 1 is a block diagram showing a construction of a driving controlling apparatus of a general linear compressor.
As shown, the driving controlling apparatus of a linear compressor comprises a linear compressor 3 for controlling a refrigerating capacity by varying a stroke (a distance between an upper dead point of and a lower dead point of a piston) by a reciprocation of a piston by a stroke voltage; a current detecting unit 4 for detecting a current applied to the linear compressor 3 by varying a stroke; a voltage detecting unit 5 for detecting a voltage generated at the linear compressor 3 by varying a stroke; a microcomputer 6 for calculating a stroke by using a current and a voltage detected from the current detecting unit 4 and the voltage detecting unit 5, comparing the calculated stroke with a user's input stroke command value, and outputting a switching control signal; and an electric circuit unit 1 for switching an alternating current by a triac 2 by the outputted switching control signal and applying a stroke voltage to the linear compressor 3.
A controlling operation of the conventional linear compressor will be explained as follows.
First, the electric circuit unit 1 outputs a stroke voltage by the user's set stroke command value, and a piston reciprocates by the stroke voltage. Accordingly, a stroke is varied and thus a refrigerating capacity of the linear compressor 3 is controlled. That is, a refrigerating capacity of the linear compressor 3 is controlled in accordance with a stroke is varied by a reciprocation of a piston inside of a cylinder and cooling gas inside of the cylinder is discharged to a condenser through a discharge valve.
When the stroke is varied by a stroke voltage, the current detecting unit 4 and the voltage detecting unit 5 detect a voltage and a current generated at the linear compressor 3 and the microcomputer 6 calculates a stroke by using the detected voltage and current.
According to this, when the calculated stroke is less than a stroke command value, the microcomputer 6 outputs a switching control signal which lengthens an ON period of the triac thus to increase a stroke voltage applied to the linear compressor 3. Also, when the calculated stroke is greater than a stroke command value, the microcomputer 6 outputs a switching control signal which shortens the ON period of the triac thus to decrease a stroke voltage applied to the linear compressor 3.
FIG. 2A is a waveform of an input voltage and an input current in case that a load is less in a driving controlling method of a linear compressor in accordance with the conventional art, and FIG. 2B is a waveform of an input voltage and an input current in case that a load is great in a driving controlling method of a linear compressor in accordance with the conventional art.
As shown in FIGS. 2A and 2B, in the conventional stroke controlling method, a firing angle (current flowing time per alternating current one cycle) according to a load applied to the linear compressor (for example, external air temperature of a refrigerator or a temperature of a condenser) is constant, so that an upper limitation point of a piston inside of a cylinder or a position where a cylinder volume is minimized are changed in accordance with that a load of a refrigerator becomes great or less.
For example, when a load less than a peripheral temperature 30° C. is less (or a load of a middle temperature state), a phenomenon that a position of a piston is changed is scarcely generated. However, when a load more than a peripheral temperature 40° C. is great (or a load of a high temperature state), a stroke is controlled by a constant firing angle (or the same input state). Accordingly, a movement distance of a piston is relatively increased in a suction processing than in a compression processing thus to generate a phenomenon that a piston is pushed backwardly, thereby generating abrasion and collision of a piston.
According to this, at the time of driving the conventional linear compressor, a phenomenon of a refrigerating capacity deficiency is generated or efficiency is lowered thus to degrade a reliability.